TWELVE LINES OF EVIDENCE FOR
THE EVOLUTION OF HUMANS
& OTHER PRIMATES

Martin Nickels
Anthropology Program
Illinois State University

ENSI Co-Director

The following outline
was adapted from a presentation, with slides, at a symposium
Teaching Evolution (and Confronting Creationism) in the College
Classroom at the meetings of the American Association of
Physical Anthropologists, Salt Lake City, Utah, April 3, 1998.
It was also presented at the Convention for the National Association
of Biology Teachers in Reno, NV, November 4, 1998, and in somewhat
abbreviated form at the NABT Convention in Ft. Worth, TX, October
28, 1999.

The full text of his presentation
was published as "Humans As a Case Study for the
Evidence of Evolution" in the Reports of the National
Center for Science Education 18(5), Sep/Oct, 1998, pp.24-27.
This FULL TEXT follows the outline below.LINKS TO TWO SLIDES (Pelvis Slide & Larynx Slide)....Scroll
down to number 5 in outline.

2. COMPARATIVE ANATOMY
- homologies
- general adaptive attributes of all primates (including humans)
- anatomy of all primates reflects arboreal adaptations
- distinctive brachiating anatomy possessed by apes and humans
(collectively the hominoids)
- anatomy of hominoids most similar to one another

3. COMPARATIVE EMBRYOLOGY (Ernst Haeckel)
- great similarity of primates and humans early in ontogeny

- suspension-bridge spine of tetrapods converted
to our less-efficient load-bearing-column spine.
- pelvic structure
adapted both for fully erect bipedalism AND giving birth to big-brained
babies.
- lowered larynx an
adaptation for speech BUT also a liability in that it makes us
more likely to choke compared to other mammals.

7. BIOGEOGRAPHY
- the geographical distribution of similar-looking species is
typically limited
- refers to the geographical distribution of similar species
as a result of shared ancestry
- examples: ., lemurs on Madagascar, New World and Old World
monkeys, lesser apes
- Darwin's 1871 prediction about finding fossils of early humans
in Africa
- gorillas, chimpanzees, bonobos and humans in Africa
- [See lesson on Island
Biogeography & Evolution]
- [Also, see lesson on A Step in Speciation - students plot the ring species of California Salamander in a north-to-south double gradient of sub-spp. separated by the Central Valley of California, ending with two different spp. in Southern California.]
- [Also, see the Quick Speciation activity, where students experience biogeography in their classroom.]

9. HOMININ FOSSIL SEQUENCE & PATTERN
- more "primitive" (less modern forms) found earlier
and before more "evolved" (more modern) forms
- the collection as of 10-99 (added for the NABT Convention in
Ft. Worth, TX):

12. CHRONOLOGICAL SEQUENCE OF STONE TOOLS- the same sort of developmental sequence seen in more "primitive"
to more "advanced" fossils is also seen in the archeological
sequence of stone tools from cruder to more sophisticated and
refined.

Humans As a Case Study for the Evidence of Evolution
by Martin Nickels, Illinois State University
NCSE Reports, vol.18, no.5, Sep/Oct, 1998, pp.24-27

As physical anthropologists we are either blessed or cursed
when it comes to teaching about evolution. The reason for the
dilemma is that, on the one hand, we focus on the organism that
is clearly the most problematic and difficult for many people
to accept as having evolved and, on the other hand, we deal with
the species that is probably unparalleled in terms of the sheer
amount of scientific information and evidence supporting the
idea that evolution has occurred on this planet.

Personally, I regard our focus on human evolution as an unparalleled
and golden opportunity for teaching about evolution and addressing
important aspects of the creation - evolution controversy. There
are several reasons for this.

First, we get to deal with the organism that more people
and students are most inherently interested in than any other:
themselves. This means that we can take advantage of this interest
and use it to deal with one of the most important ideas in all
of science, namely evolution.

Second, because of the amount of scientific evidence
that exists for human evolution, we are in the enviable position
of being able to draw upon knowledge from many areas of scientific
research and build one of the strongest cases for evolution in
all of biology.

Third, because of our primary focus on humans, we can
underscore and reinforce the idea that humans are indeed animals
(that is to say, we are a part of the natural world rather
than a creature set apart from it. This idea becomes even
more important, of course, when we make the case that humans
are a natural product of biological processes.

Fourth, by making the case convincingly for human evolution,
we pretty much assure that making the case for any other species
will be that much easier. After all, having already dealt with
the single most problematic species of all, there can't be too
many objections to thinking that other - indeed all other - organisms
have also evolved.

Fifth, we have the opportunity to illustrate several
important aspects of the nature of science and scientific knowledge.
These include using such criteria as independent lines of evidence,
concordance or consistency of evidence and the predictive power
found in the patterns inherent in nature to advance scientific
understanding of the world we live in and have emerged from.

The focus of this discussion is to illustrate both the strength
of the many lines of scientific evidence supporting the idea
of human evolution and the importance of the concordance or agreement
that exists among them. Some of the most important criteria by
which the strength of any scientific theory is assessed include
the number of independent lines of evidence that are concordant
with one another and the ability to use knowledge of one line
to predict the pattern we should find in another. Thus, using
humans as a case study in evolution also allows us to illustrate
some broader aspects of the nature of science and how one can
judge the overall strength of any scientific theory or explanation.

I want to underscore the importance of using the term "evidence"
rather than the more colloquial term "proof" in normal
scientific discourse. Scientists deal with evidence, not proof,
in the sense that we deal with information and data that must
be made sense of or interpreted rather than being, pardon the
expression, self-evident. Mathematicians and logicians may deal
in undeniable proof because of the nature of the abstract ideas
and concepts that they deal with, but scientists must discover
the patterns inherent in the natural world and then explain them
in light of our understanding of the natural processes that we
must use to account for those patterns.

Scientists have, in turn, developed criteria to assess and
evaluate the relative merits of alternative explanations of the
evidence. These criteria include valuing concordance among independent
lines of evidence and the ability to predict one line of evidence
from another as ways to distinguish better explanations from
worse ones.

Now, let me turn to 12 lines of Evidence for Human Evolution.
I've grouped them into 7 that represent evidence from the biological
present and 5 that represent evidence from the geological and
biological past. I will make observations about their significance
and inter relatedness rather than explain what each line means
since I think they're mostly self-explanatory in that regard.

Category Number 1 (Hierarchical Taxonomic Classification)
is a good example of a pattern that can, of course, be explained
by special creation. Linnaeus did just that. But Darwin - a century
later - explained the same set of orderly relationships between
organisms as being the result of divergent evolution and shared
ancestry. More important, though, is the fact that organisms
created de novo need not show varying degrees of similarity
to one another. Each creature could be constructed completely
differently from every other creature and made from very different
materials. Humans need not look like apes, but we do. We show
varying degrees of similarity to them and we are made of the
same stuff. We could have been created this way but we
must look like this if, indeed, we have evolved and diverged
from a relatively recent common ancestor.

Another important and seldom appreciated characteristic of
the evolutionary explanation for the existence of organisms in
naturally nested or hierarchical groupings is that it allows
us to predict that organisms with certain combinations of features
- such as chimpanzees with wings, flowers with bony skeletons,
or humans with hooves instead of feet - are biologically impossible
because of the unbridgeable gaps produced by the major divergent
evolutionary events that separate chimps from birds, flowers
from vertebrates, and humans from horses. An all-powerful creator,
of course, could create almost any combination of such fantastic
and fanciful creatures.

"It is indeed remarkable that this
theory has been progressively accepted by researchers, following
a series of discoveries in various fields of knowledge. The convergence,
neither sought nor fabricated, of the results of work that was
conducted independently is in itself a significant argument in
favor of this theory."
Pope John Paul II addressing the Pontifical Academy of Sciences
on October 22, 1996.

Number 2 (Comparative Anatomy) and Number 3 (Comparative
Embryology) are similar to Number 1 in that organisms could
have been deliberately formed to resemble one another but they
need not have been. But if organisms share varying degrees of
evolutionary kinship with one another, then such anatomical and
embryological similarities are mandatory. There is probably no
more powerful or striking example of such similarity than that
seen among the fetuses of primates, especially the hominoids.

Category Number 4 (Comparative Biochemistry)
is of special interest and importance. This is due to the fact
that the agreement or concordance of the biochemical evidence
with the anatomical evidence illustrates another important consideration
when evaluating the strength of evolutionary theory: namely that
our 20th century ability to compare the biochemical similarities
among species provided a test of evolutionary theory which had
been mainly based on the evidence from 19th century comparative
anatomical studies, biogeography and a very limited fossil hominin
record. If the same overall pattern of biochemical similarities
did not agree with the pattern based on anatomical comparisons,
evolutionary theory would have been in serious trouble. But the
patterns do agree and evolutionary theory is all the stronger
because of that.

Number 5 (Adaptive Compromises) and Number 6 (Vestigial
Structures) are both very difficult to explain as being the
result of deliberate design or special creation since they represent
such "poor" engineering. But they are exquisite examples
of the constraints inherent in biological systems evolving over
time and having only existing ancestral structures available
for modification in the face of new and often competing selective
pressures. The human examples I've listed under Number 5 - the
pelvis and the larynx - are two of the
better examples of adaptive compromises between competing selective
pressures that I know of.

Item Number 7 (Biogeography) refers simply to the observed
fact that similar-looking species tend to be found in close proximity
to one another - as illustrated by the primate examples I've
listed. The special case of biogeography pertinent to human evolution,
of course, is that in 1871 Darwin used the work of Huxley and
others which showed that humans most resemble chimpanzees and
gorillas who live only in Africa to predict where we would most
likely find fossils of our own earliest ancestors - Africa.

That Darwin was correct is borne out by Category Number
8 (Paleobiogeography) as, indeed, all of the earliest-known
hominins are from Africa and nowhere else. But the fact that
Darwin could use evidence from biogeography to predict what the
pattern should look like in a completely separate body of evidence
- the fossil record - is a wonderful example of how concordance
among separate lines of evidence is both a testable prediction
of a scientific theory and further support for a theory - in
this case, evolution - when the prediction is borne out.

Number 9 (the Fossil Sequence) for hominins is just
a single case study of the general pattern present in the overall
fossil record. That pattern is that modern species are not found
throughout the fossil record from top to bottom - which they
should be if all species were formed at one time at the very
beginning of life on this planet. Instead, what we discover is
less and less evidence of modern species as we go deeper and
deeper into the fossil and geological record - a pattern both
predicted by evolutionary theory and completely consistent with
evolutionary theory. Indeed, this is the only pattern
consistent with evolutionary theory. And there is no more impressive
fossil series one can use to illustrate this pattern than the
overall hominin fossil sequence. There is also no more pedagogically
powerful example for students than that of our own lineage.

Number 10 (Fossil Intermediates) refers
to the fact that, regardless of the mode or rate of evolutionary
change, there should be evidence of morphological continuity
over time in the fossil record if species are evolutionarily
linked and related to one another. Is there a better classroom
example one can use to illustrate this point than a fossil like
Lucy with her mixture of ape-like and human-like features? I
sometimes think that as physical anthropologists we are especially
blessed to have such a wonderful example to use in our teaching.

Number 11 (the Ecological Coherence of Fossil
Assemblages) is an especially powerful point to use when
countering the associated claims of Flood Geology that many creationists
make. The idea that the fossil and geological pattern seen on
this planet is really a record of a single, recent, global catastrophe
in the form of the Great Deluge and Flood postulates that no
real chronological order of any consequence exists in the earth's
geological or fossil record. But the fact that successive fossil
assemblages actually contain ecologically-coherent groups of
species common to specific environments counters this creationist
claim by illustrating that environments come and go and come
again many times over time but the species within them change.

The fossil record, then, is not merely a jumbled collection
of drowned flood victims but a record consisting of ecological
snapshots of the natural history of life on this planet. The
number of ecologically-coherent paleoanthropological and archeological
sites from Laetoli, Lake Turkana, Olduvai Gorge on up to the
present is stunning, and all provide excellent examples for us
to use in our teaching.

Finally, Number 12 (the Archeological Record) of stone
tools and other artifacts is a uniquely human line of evidence
available to us because we teach about human natural history.
No other organism has left such a record of its behavioral evolution.
More importantly, the pattern of change in the lithic prehistory
of humans parallels that of the fossil record in its change from
more primitive to more modern over time. The archeological record
uniquely enriches our study of human evolution.

Individually, perhaps, one can claim that any given line of
evidence looks the way it does because that is the way it was
intended to look by a/the Creator. But such a creationist claim
actually involves mixing elements of different creationist models
such as the "young earth - quick creation with a flood"
model and the "old earth - progressive creation without
a flood" model in ways that are fundamentally incompatible
and inconsistent with one another. Only an evolutionary explanation
can rationally account for these lines of evidence both individually
and collectively. Indeed, it is their combined strength that
supports evolution so extraordinarily well.

In conclusion, the fact that there are so many lines of evidence
in support of the idea of human evolution simply means that we,
as physical anthropologists, have an unrivaled opportunity to
teach about evolution and effectively confront creationism in
our classrooms. We have the best case study for evolution in
all of biology. Let us rejoice in that and use it in our teaching.
The opportunity is yours, and I hope you all take advantage of
it.

Acknowledgment: Many thanks to Craig Nelson of Indiana
University for helping me develop and enrich my thinking about
the strength of the case for evolution in general. He encouraged
me to apply several of these lines of evidence to humans as a
case study.

-----------------
This article was adapted from a paper presented in the symposium
Teaching Evolution (and Confronting Creationism)
in the College Classroom at the meetings of the American
Association of Physical Anthropologists, Salt Lake City, Utah,
April 3, 1998.

Martin Nickels is Professor of Physical Anthropology at
Illinois State University in Normal. His
research interests include the history of human evolutionary
studies, hominin paleontology and prehistory, primate behavior,
and the biological bases of human behavior: He twice was selected
as the Outstanding University Teacher at Illinois State University
and was a Sigma Xi National Lecturer in 1995 and 1996. He co-authored
The Study of Physical Anthropology and Archaeology, as well
as articles in many professional journals.